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学术论文

Ming-Yang He, Hong-Bo Liu*, Bin Wang, and Da-Lin Zhang.J. Appl. Meteor. Climatol.:2016,55(1),41-60摘要In this study, the three-dimensional structures and diurnal evolution of a typical low-level jet (LLJ) with a maximum speed of 24 m s−1 occurring in the 850–800-hPa layer are examined using both large-scale analysis and a high-resolution model simulation. The LLJ occurred on the eastern foothills of the Yun-Gui Plateau in south China from 1400 LST 29 June to 1400 LST 30 June 2003. The effects of surface radiative heating, topography, and latent heat release on the development of the LLJ case are also studied. Results show that a western Pacific Ocean subtropical high and a low pressure system on the respective southeast and northwest sides of the LLJ provide a favorable large-scale mean pressure pattern for the LLJ development. The LLJ reaches its peak intensity at 850 hPa near 0200 LST with wind directions veering from southerly before sunset to southwesterly at midnight. A hodograph at the LLJ core shows a complete diurnal cycle of the horizontal wind with a radius of 5.5 m s−1. It is found that in an LLJ coordinates system the along-LLJ geostrophic component regulates the distribution and 65% of the intensity of LLJ, whereas the ageostrophic component contributes to the clockwise rotation, thus leading to the formation and weakening of the LLJ during night- and daytime, respectively. Numerical sensitivity experiments confirm the surface radiative heating as the key factor in determining the formation of the nocturnal LLJ. The existence of the Yun-Gui Plateau, and the downstream condensational heating along the mei-yu front play secondary roles in the LLJ formation.

Modeled responses of summer climate to realistic land use/cover changes from the 1980s to the 2000s over eastern China

Hu, Y., X.-Z. Zhang, R. Mao, D.-Y. Gong, H.-B. Liu, and J. Yang.Journal of Geophysical Research:2014,doi: 10.1002/2014JD022288摘要下载全文Eastern China has experienced substantial agricultural expansion and deforestation in recent decades. We modeled the influence of land use/cover changes (LUCCs) over eastern China on the regional climate using the Weather Research and Forecasting (WRF) model with the Noah-MP land surface scheme. Two 21-year (1980-2000) experiments were performed using the same settings, except for the land use/cover data for the 1980s and 2000s. The results showed that in northern China, decreases in the surface air temperature of approximately 0.3~0.5 °C and decreases (increases) in rainfall over the lower reaches of the Yangtze River valley (southern China, northeastern China and the Korean Peninsula) of approximately 3 % (6~7 %) in the summer were associated with LUCCs in eastern China from the 1980s to 2000s. The cooling effect in northern China, which was primarily attributable to an increase in the surface latent heat flux of approximately 7.3~9.6 W m-2
, weakened the land-ocean thermal contrast, suggesting the presence of a weaker summer monsoon over eastern China. As a result, rainfall over the lower reaches of the Yangtze River valley (southern China) tended to decrease (increase). In addition, the cooling effect may have produced an anomalous cyclonic circulation from the surface to the mid-troposphere over northeastern China and the Korean Peninsula, resulting in increased rainfall over this area.

Liu Hongbo，He Mingyang，Wang Bin，Zhang Qinghong.Journal of Meteorological Research:2014,28(1),057-075摘要下载全文The low-level jet (LLJ) is closely related to severe rainfall events, air pollution, wind energy utilization,
aviation safety, sandstorms, forest ¯re, and other weather and climate phenomena. Therefore, it has attracted considerable attention since its discovery. Scientists have carried out many studies on LLJs and made significant achievements during the past five or six decades. This article summarizes and assesses the current knowledge on this subject, and focuses in particular on three aspects: 1) LLJ classification, definition, distribution, and structure; 2) LLJ formation and evolutionary mechanisms; and 3) relationships between LLJ and rainfall, as well as other interdisciplinary fields. After comparing the status of LLJ research at
home (China) and abroad, we then discuss the shortcomings of LLJ research in China. We suggest that this includes: coarse definitions of the LLJ, lack of observations and inadequate quality control, few thorough explorations of LLJ characteristics and formation mechanisms, and limited studies in interdisciplinary fields.
The future prospects for several LLJ research avenues are also speculated.

Roles of synoptic to quasi-biweekly disturbances in generating the summer 2003 heavy rainfall in East China

Liu, H.-B., J. Yang, D.-L. Zhang, and B. Wang.Monthly Weather Review:2014,Vol. 142, No. 2,886-904摘要下载全文During the Meiyu season of summer 2003, the Yangtze and Huai River Basin (YHRB) encountered anomalously heavy rainfall, and the northern YHRB (nYHRB) suffered a severe flood because of five continuous extreme rainfall events. A spectral analysis of daily rainfall data over YHRB reveals two dominant frequency modes: one peak on day 14 and the other on day 4, i.e., the quasi-biweekly and synoptic-scale mode, respectively.
Results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies, respectively, to the Meiyu frontal convergence over southern YHRB (sYHRB) at the peak wet phase. An analysis of band-pass filtered circulations shows that the lower and upper troposphere was fully coupled at the quasi-biweekly scale, and a lower-level cyclonic anomaly over sYHRB was phase-locked with an anticyclonic anomaly over the Philippines. At the synoptic scale, the strong northeasterly components of an anticyclonic anomaly with a deep cold and dry layer helped generate the heavy rainfall over sYHRB. Results also indicate the passages of five synoptic-scale disturbances during the nYHRB rainfall. Like the sYHRB rainfall, these disturbances were originated from the periodical generations of cyclonic and anticyclonic anomalies at the downstream of Tibetan Plateau. The nYHRB rainfalls were generated as these disturbances moved northeastward under the influence of monsoonal flows and higher latitude eastward-propagating Rossby-wave trains. It is concluded that the sYHRB heavy rainfall resulted from superposition of quasi-biweekly and synoptic-scale disturbances, whereas the intermittent passages of five synoptic-scale disturbances led to the flooding rainfall over nYHRB.

Low-level jets over southeast China: warm season climatology for the summer of 2003

Liu, H., L. Li, and B. Wang.Atmospheric and Oceanic Science Letters:2012,5,394-400摘要下载全文The southwesterly low-level jet (LLJ) over
southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data on 1.0×1.0-degree grids at 6-h intervals. The major criteria for choosing the LLJ included the following: a maximum wind speed equal to or greater than 12.0 m s–1, a wind direction of between 180° and 270°, and the height of wind maximum at 900–700
hPa, not confined to single pressure level. The results show that the LLJs over southeast China dominate at 850 and 800 hPa. These LLJs are closely associated with the topography of this area and tend to locate regions with large terrain gradients, including the northeastern and eastern Yunnan-Guizhou Plateau. Under the influence of mid-latitude westerly winds, the LLJs above 750 hPa move northward to the Yangtze-Huai River Basin. Compared to the ten-year (2000–2009) mean climate conditions, the LLJs in the warm season of summer 2003 were exceptionally active and strong, as reflected by the positive anomalies of LLJ occurrence numbers and wind
speed. In addition, the 2003 LLJs showed strong diurnal variation, especially at pressure levels below 800 hPa.
The majority of the LLJs appeared between midnight and
the early morning hours (before 8 a.m.). Finally, the
summary of LLJ grid numbers indicates that more than 80% of LLJs in June and July 2003 occurred within the
33-d rainy period. Thus, these LLJs are directly related to
the anomalously heavy rainfall in the Yangtze-Huai River
Basin.

Numerical simulation of the heavy rainfall in the Yangtze-Huai River Basin during summer 2003 using the WRF Model

Liu, H..Atmospheric and Oceanic Science Letters:2012,5,20-25摘要下载全文In this study, a 47-day regional climate simulation
of the heavy rainfall in the Yangtze-Huai River Basin
during the summer of 2003 was conducted using the
Weather Research and Forecast (WRF) model. The simulation
reproduces reasonably well the evolution of the
rainfall during the study period’s three successive rainy
phases, especially the frequent heavy rainfall events occurring
in the Huai River Basin. The model captures the
major rainfall peak observed by the monitoring stations in
the morning. Another peak appears later than that shown
by the observations. In addition, the simulation realistically
captures not only the evolution of the low-level
winds but also the characteristics of their diurnal variation.
The strong southwesterly (low-level jet, LLJ) wind speed
increases beginning in the early evening and reaches a
peak in the morning; it then gradually decreases until the
afternoon. The intense LLJ forms a strong convergent
circulation pattern in the early morning along the Yangtze-
Huai River Basin. This pattern partly explains the
rainfall peak observed at this time. This study furnishes a
basis for the further analysis of the mechanisms of evolution
of the LLJ and for the further study of the interactions
between the LLJ and rainfall.

Liu, H., and B. Wang.Meteorology and Atmospheric Physics:2011,114,doi: 10.1007/s00703-011-0143-y摘要下载全文In this paper, a comparison study of three
cumulus parameterization schemes (CPSs), Kain-Fritsch2
(KF2), Grell (GR) and Anthes-Kuo (AK), is carried out
using the Pennsylvania State University-National Center
for Atmospheric Research mesoscale model (i.e., MM5).
The performances of three CPSs are examined in simulations
of the long-term heavy Meiyu-frontal rainfall
events over the middle to lower reaches of the Yangtze
River Basin (YRB-ML) during the summer of 1998. The
initial and lateral boundary atmosphere conditions are
taken from the National Centers for Environmental Prediction/
Department of Energy Reanalysis-2 (R-2) data.
The experiment with KF2 scheme (EX_KF2) reproduces
reasonably well the major rainfall events, especially the
heavy rainfall over YRB-ML during the later stage, and
the middle and lower troposphere circulation patterns. In
contrast, the experiments with both GR and AK schemes
(EX_GR and EX_AK) only simulate the heavy rainfall
during the first Meiyu rainy phase with weak intensity,
and almost miss the rainfall along YRB-ML during the
second phase. The analyses show that the location of
500 hPa western Pacific subtropical high during the first
rainy phase, the northward advance during the transition
period and the retreat during the second rainy phase,
observed from the R-2 data, are successfully captured by
EX_KF2, compared to the poor performance of EX_GR
and EX_AK. A reasonable proportion of the subgrid-scale
rainfall and smaller biases of temperature and moisture
from lower to middle troposphere in EX_KF2 decide its
good rainfall simulations, in contrast with the absolutely
high proportions and the cold and dry biases caused by
the decreased vertically convective transportation and the
weak southwesterly wind in EX_GR and EX_AK. Overall,
the three CPSs show substantial intersimulation differences
in rainfall as well as in three-dimensional
atmospheric structures, and KF2 shows superior performances.
The results suggest that the realistic subgrid-scale
CPS is still highly required for the high-resolution
regional climate models to simulate the heavy rainfall
events.

Impact of horizontal resolution on the regional climate simulations of the summer 1998 extreme rainfall along the Yangtze-River Basin

Liu, H., D.-L. Zhang, and B. Wang.Journal of Geophysical Research:2010,115,D12115, doi:10.1029/2009JD 012746摘要下载全文In this study, the effects of varying horizontal grid resolutions on the regional climate
model (RCM) simulation of the summer 1998 extreme rainfall events along the middle
to lower reaches of the Yangtze‐River Basin (YRB‐ML) are examined using the
Pennsylvania State University‐National Center for Atmospheric Research mesoscale
model (i.e., MM5). Results show that the MM5 simulation with the finest grid size of 4 km
reproduces reasonably well the rainfall intensity and rainbelt distribution over the
YRB‐ML during all the Meiyu phases, whereas lower‐resolution simulations tend to shift
the east‐west‐oriented major rainbelt southwestward as a result of the generated local
storms and excessive rainfall during the second Meiyu rainy phase in which vertical
(horizontal) wind shears are weak (strong). The excessive rainfall occurs during the
evening hours when the low‐level jet is relatively strong and in the Meiyu frontal zone
where convergence of warm and moist air is pronounced. Results reveal the importance of
incorporating convective parameterizations in removing potential instability in heavy
rain‐producing storms even for RCMs with 3–5 km horizontal resolutions. It is highly
desirable to use higher‐resolution models with realistic parameterized and grid‐scale cloud
physics schemes to study the regional climate of heavy rainfall events.

Daily to submonthly weather and climate characteristics of the summer 1998 extreme rainfall over the Yangtze River Basin

Liu, H., D.-L. Zhang, and B. Wang.Journal of Geophysical Research:2008,113,D22101, doi:10.1029/2008JD010072摘要下载全文In this study, the daily to submonthly weather and regional climate characteristics
associated with the extreme rainfall events over the middle to lower reaches of the Yangtze
River Basin (YRB-ML) during the summer of 1998 are examined using the National
Centers for Environmental Prediction/Department of Energy Reanalysis-2 data and a
54-day high-resolution (i.e., Dx = 4 km) simulation with a regional climate model
(RCM). As verified against various observations, the RCM reproduces reasonably well the
accumulated daily to biweekly rainfall events, their generation and subsequent evolution
along the Meiyu front, and especially the rainfall events over the YRB-ML during the later
stage of the 1998 floods. It is found that the early stage of the 1998 floods resembles in
many aspects that occurred in normal years, except for a moister-than-climate state
and stronger-than-normal low-level jets (LLJs) in Southeast China, whereas the later stage
exhibits two abnormal height anomalies to the northeast and southwest of the YRB-ML,
facilitating convergence of northeasterly and southwesterly flows along the Meiyu front.
It is also found that the Meiyu front weakens in depth and intensity as it migrates
northward across and then retreats to the YRB-ML, playing less important roles in rain
production. Results show different daily to biweekly rainfall characteristics at the different
stages, e.g., from eastward propagation to local generation of mesoscale convective
systems and periodical rain production along the Meiyu front, most of which reach their
maximum intensities over the YRB-ML during the morning to early afternoon hours.
Results indicate that the northeasterly moisture supply enhances the production of steady
heavy rain at the later stage of the 1998 floods. It is concluded that the West Pacific
subtropical high and the Meiyu front control the general areas of rain production, the lowlevel
moisture supply through LLJs and mesoscale disturbances determines whether or not
sustaining flooding rains would occur, and what rainfall characteristics are at the daily to
biweekly timescales.